The Great Symbian

Thread Library schedules user-level threads to run on LWP

Thread management done by user-level Threads Library

The Thread Library is responsible for scheduling user threads on the available schedulable entities; this makes context switching of threads very fast, as it avoids system calls. However, this increases complexity and the likelihood of priority inversion, as well as suboptimal scheduling without extensive (and expensive) coordination between the userland scheduler and the kernel scheduler.